Formerly, in order to mix and homogenize pourable materials to be ground, particularly raw components for the foodstuff and feedstuff industries. the so-called batch mixer was used almost exclusively. These batch mixers enable a thorough mixing and a high degree of homogeneity with respect to all raw components, even the smallest, e.g. for the production of a baking mixture. In practice, there are a great number of concepts having particular characteristics depending on the technical field. In the simplest solution, the batch mixer is constructed simultaneously as a hopper scale. The required raw components are weighed in one after the other, according to a predetermined recipe, by means of the weight signals and are subsequently homogenized with the mixing tools comprehending the entire batch container. The homogeneity can be controlled advantageously in this instance by means of a suitable construction of the mixing tools and optimal time period. However, there are two fundamental disadvantages to this solution. Firstly, a discontinuous operation results from the sharp separation of work cycles:
metering--weighing PA1 mixing--homogenization PA1 discharging
Secondly, the volume of the batch mixer, e.g. one to two cubic meters, and the time required for a mixing and homogenizing cycle determines the quantity which can be mixed per hour. Strict limits are accordingly imposed on increases in output.
Attempts have been made to reduce these disadvantages in various ways, e.g. in that at least a portion of the raw components are added simultaneously by means of metering weighers. A genuine increase in output can accordingly be achieved by using a preliminary container weigher in which a new mixture is prepared completely according to the recipe during the homogenization process and can be discharged into the batch mixer within several second. Moreover, the time required for discharging can be shortened when a secondary container of the same proportions as the batch mixer is arranged subsequent to the latter, an entire batch being discharged into the secondary container in each instance. A continuous product flow can thus be delivered from the secondary container via discharging elements. Thus, a high construction cost is required for the continuous delivery of a homogenized product with high hourly output, since a certain overall height or building height is required in order to arrange the three containers one below the other so that the transfer of product can be effected by means of gravity. If product mixtures which are processed one after the other may not be contaminated or if very strict demands are made with respect to hygiene, a thorough cleaning must be performed periodically and certain residues must be removed from the containers, if necessary, after every change of mixture.
Recently, in order to reduce these disadvantages somewhat, continuous systems have been used to an increasing extent. Solutions with belt weighers are known. So far, it has not been possible for this system to prevail in a broader market or to partially displace the batch mixer. Hygiene could be improved only in part. The homogeneity is not as good as in the batch mixer in every case, but in particular the investment cost for belt weighers is considerable in many cases. Simple metering elements such as those used for liquids or for freely flowing grain product cannot be used because of the poor flowing properties of at least a portion of the components or materials to be ground.